Abstract

We previously showed that striated muscle-selective depletion of lamina-associated polypeptide 1 (LAP1), an integral inner nuclear membrane protein, leads to profound muscular dystrophy with premature death in mice. As LAP1 is also depleted in hearts of these mice, we examined their cardiac phenotype. Striated muscle-selective LAP1 knockout mice display ventricular systolic dysfunction with abnormal induction of genes encoding cardiomyopathy related proteins. To eliminate possible confounding effects due to skeletal muscle pathology, we generated a new mouse line in which LAP1 is deleted in a cardiomyocyte-selective manner. These mice had no skeletal muscle pathology and appeared overtly normal at 20 weeks of age. However, cardiac echocardiography revealed that they developed left ventricular systolic dysfunction and cardiac gene expression analysis revealed abnormal induction of cardiomyopathy-related genes. Our results demonstrate that LAP1 expression in cardiomyocytes is required for normal left ventricular function, consistent with a report of cardiomyopathy in a human subject with mutation in the gene encoding LAP1.

Figure 1. Analysis of hearts of M-CKO mice with striated muscle-selective depletion of LAP1. (A) Protein extracts from hearts of control (Tor1aip1f/f) and M-CKO mice with striated muscle depletion of LAP1 were used for immunoblotting with antibodies against LAP1 and GAPDH antibodies. Each lane contains an extract from a different mouse. (B) Representative transthoracic M-mode echocardiographic tracing of control and M-CKO male mice at 9–10 weeks of age. (C) Left ventricular end-systolic diameter (LVESD) and fractional shortening (FS) in control (n = 9) and M-CKO (n = 10) male mice at 9–10 weeks of age. Each circle and triangle represents a value from individual mice, and the horizontal bars indicate means. (D) Means ± standard errors of relative expression of mRNAs encoded by NppA and NppB in hearts of control (n = 4) and M-CKO (n = 4) mice at 12 weeks of age. *P < 0.05; **P < 0.01.

Figure 3. Generation and characterization of H-CKO mice with cardiomyocyte-selective depletion of LAP1. (A) Protein extracts from hearts and skeletal muscles (Sk. muscle) from control (Tor1aip1f/f), H-CKO and M-CKO mice were used for immunoblotting with antibodies against LAP1 and GAPDH. LAP1 isoforms were detected by the anti-LAP1 antibody. Each lane contains an extract from a different mouse. (B) Micrographs showing immunofluorescence labeling of LAP1 (red) and α-actinin (green) in left ventricle sections from control and H-CKO mice. Nuclei were stained with 4’,6-diamidino-2-phenylindole (blue). Bar = 10 μm (C) Micrographs showing immunofluorescence labeling of lamin A and C (lamin A/C, red) and lamin B1 (red) on cross sections of heart from control and H-CKO mice. Nuclei were stained with 4’,6-diamidino-2-phenylindole (blue). Bar = 10 μm. (D) Micrographs of hematoxylin and eosin-stained cross sections of quadriceps muscle from control, H-CKO at 20 weeks of age and M-CKO male mice at 12 weeks of age. Bar = 50 μm